Electrical network



5 Sheets-Sheet l Filed NOV. 14, 1930 Iggy.

July 25, 1933. M. vos ET A. 1,920,041

ELECTRICAL NETWORK Filed Nov. 14, 1930 5 Sheets-Sheet 2` July 2s, 1933. M. vos Em. y 1,920,041

ELECTRICAL NETWORK Filed -Nov. 14, 1930 5 Sheets-Sheet 5 iwf/a 6 July 25, 1933. M. vos Er Al.

ELECTRICAL NETWORK 1950 5 AShee-Sheec. 4

Filed NOV. 14,

July 25, 1933. M. vos ET AL ELECTRICAL NETWORK Filed Nov. 14, 1930 5 Sheets-Sheet 5 .nrauni'rz vos Ann Tonnen LAURENT, er sfreainonivi, swnnnnnssienons'lo TELE- ronnnrrnnornenr n. M. @Bresson or srocnncmi, SWEDEN, n COMPANY oF` Patented `iuly 25, 19373A f narran `srares swnnnn,

nnncfrniciin NETWORK Application filed November 14, 1930, Serial No. 495,74,'-and .in weden November 18, 1929.

The present invention relatesjto an impedance network.` More particularly the invention relates to such vnetworks yused in telephone lines and in.linesfforfniultiple traiiic with high frequency currents,.the network having then for its purpose to separatecun rents oi 'diiierent frequencies or of different directions of propagation. ln lines having:

repeaters the network may be used inA` connection withy differentialtransformers and balancing networks to eliminate reflection disturbances. s The networkaccordmg to tlie'invention is arranged iii/"so called bridgedl '"`connection,`

i. e.v it consists ofa shunt inductance and series inductances Ysyninietrica-ily ccnnected inrelation thereto which latter inductances twog and two are bridged by bridging impedances. The inipedances included in the network `i'orni, according to the invention, two filter comprises also the shunt. impedance whereas the other iilter chain comprises the bridge impedance or inipedances. Thecharacteristics oi the two i'ilters at the iiiternalterniinale, i. e. those connected in the network, are' adjusted to suit each otherand the line charn acteristic in a particular-manner described below. f

ialthough the network operates as ailter chain in its entirety, itishowever, by rnu tual and suitable adjustment of the filter chains rendered possibletoinake the input and the output impedances of the network independent oi the frequency in the neighbcurhccd of the limiting frequencies of the two filtu chains; Said property! is oi great importance as it renders possible afrelectioniess connection to the network operating as a iilter chain which hitherto` has not been passible.

The' inventionfrelates also to special embodi ments et the ilter chains includedin the -letvf'ork and certain arrangements and coinbinations of several similar networks-to yobtain the best possible" utilization of the incoming energy. l U

ln the application of the invention Avior multiple traic in the telegraphy and the make the line reiiectionless.

The invention will be more closelydescribed Ywith n reference to the, accompanying drawings which show a number ofdiffereiit embodiments.` Figurev ll shows: diagram-l inatically an embodiment oi the network in iinsym'nietrical4 bridged lm-connection. Figures 2 andi); show the two iilter chains included in the network according to Figurerl Vand separated from each ctlier.

l Figure a shows a' connection corresponding to thev one in Figure l but symmetrically formed. Fig-v ure 5 shows two' filter cnains oi which Vthe net has to be built. yFigure 6 shows two inipedances corresponding to each other Iin the two ilter chains f in' Figure 5. Figure 7 shows a special embodiment 'of the inipedances in` Figure 6. Figure S showsaii embodiment of the inventionin which a 'di'i fereiitial transformer is included. Figure 9 fsh'ows diagraminatically the connection offa two-wayr amplifier which lis provided with networks according tothe invention. VFigure l0 shows Va part oi a two-way amplifier as carried out in practice. Figure l1 shows a network according to the invention. Figures 12 to l5 show other embodiments of the network and Figure 16 is a circuit diagram of a sending and receiving setv for highfrequency and `lowifrequericy signals. VThe plant-comprises a Anumber of networks con- Y nected in cascade according tothe invention. -Figure l7shows anenibodiment oi a connection between a two-wire line and a loaded or .pupinized quad wire connection, the two4 talking paths in thefquadv wire connection vbeing used for mutually opposite talking di- 1 60 independently of the number of part networks coiinected in cascade, beadjusted toV ment of such a connection the two'lines in the quad wire connection being parallel connected and forming together a single talking path.

5 The network according to Figure 1 arranged in unsymmetrical bridged T-connec:

tion comprises the shunt inductance 17, the

two series impedances 1l, 12 connected symmetrically ink relation to the' shunt impedyposed `of two filter chains A, B which are shown individually in Figures 2 and 3. In

the ilterchain's the two series impedances '11 12 form a common art.V The filter chain 7 e l s a n a A comprises, inV addition yto said series impedances, the shunt impedancev lrlandv the filter chain B comprises, besides the series impedances 11, 12, thebridge impedance 18 connected in shunt thereto. The network is provided with input and output terminals l, 2 and 3, 4 andthe connections between said two'terminal couples may be considered as forming two through-going lines @,b.

with one couple of externallterniinals k7, 8 and 5, 6 respectively for the .connectionwoil branch lines or apparatus or the like, by way of example. sending and Areceiving sets. The terminals 7, 8 oi' the filter` chainfA are 'disposed onfthe 'shunt impedance 17, and the terminals 5, Gofi the filter chain B are disposed on the bridge impedance 18. The two 35: terininal'couples o, Zand e, fof the two/filter chains maybe considered as junction points. r

Theoiie 0 of the internal terminals of the filter chain Agis an imaginary Junction point necting together the external ends of the parallel connected Seriesimpedances 11,l 12. The other Z of the internal terminals ofthe filter chain Ais formed by the middle point of the'line Z).- The internal terminals of the filter chain-B may be considered as coincidj ing with th-e terminals 1, 3 of the network.

Y When carrying outtheinyention in l,practice vinipedancesof equal sizes, suchas lines or line sections, are generally` connected to` the-twoterminal .couples 1, 2 and 3, LL respectively.I As will be shown in the following it is possible, by a suitable arrangement of the two filterchains A,'B, to manage that the input and output characteristics of the 5,5 A minalsl, 2 and 3, 4, will be Vequal bothl in relation t'oeach other and in relation to theA impedances connected thereto so as to avoidv reflections at the terminals. Q0.

duced.

Xl--theimpedance of the filter Vchain A between theterminals @and CZ. A X2=the impedance of the lilter Vchain B between; the terminals c and f. i

ance, andthe bridgeiinpeda-nce 18 shunted] across the two 'series 'impedances From an electrical point of view the network is comf VThe two filter chains A, -B are each provided which may-be conceived as formed by con-` networks, thus the characteristicsat the terg The following .designations are introt f =an impedance connected into circuit bei I tweentlie terminals l and 2.

The input impedance between the terminals 3and4 may beexpressed as follows:

"It now @Tira l w we obtain according to Equation 1 c fICl-)gV It is now assumed that the one filter chain, by way of example A, counted from the internalterminals c, Z begins with. a half {iilter chain having a T-characteristic where- Vhalf T-section consists4 of a series impedance X4=S1/2 and ,a shunt impedance X3=2A1 and the half vr-section consists of a series impedance 35:52/2 and a shunt impedance y4=2A2. vThe characteristics Z1, Z2 have the following values.

i Forithe sake of sim li'city the following abbreviations are intro` uced. f

"Rm/Sa 11 R2 z 'V SZAZ \/1 *l* The following `expressions are then obtained.

Zii=R1pi` (3,)

. Z :R y,

2 *'2- (4') 125 Y P2 Y When the filter chainsiA, B are terminated refiectionless their input impedances X1, X2 are equal to the input characteristics Z1, Z.,

and theinput impedance of the networks at the terminals 3, 4c becomesthen according to (2) According to the invention filters are used possible to eliminate said two root expressions from the formula of the network impedance according `to (5) said impedance will be independentof the frequency. Said result may be obtain-ed by selecting the series iinpedances and the shunt impedances of the filter chains A, B in such a manner that film@ aus S1 S2 (e) y P1 P2 v iiccordingto the Formula (5) we obtain VZ: 4\/Z1Z2= v R132 (7) rlChe input impedance of the network will thus be constantand equal to a purely ohmic resistance.

It is not necessary thatk the two filter chains directly begin with a lsection or Va w-section. There are filters, by way of example according to the Swedish patent application No. 965/28 which may have T or 'fr-characteristic Without externally appear ing as beginning with. a `lsection or a n--section.

Besides the condition that the two filter chains A and B should have opposite characteristics at their internal terminals it is assumed, according tothe theory' offilter chains, that the two filter chains have the same limiting frequency. 'llhe condition that the filter' chains terminate reflectionless must not always be complied with which will be explained in the .following with reference to Figure 5. l

Under said. conditions also the input inn pedance of the network is independent of the frequency also in the neighborhood of the limiting frequency of the two filter chains.

`When this result is obtained one may easily, by the addition of suitable impedances, obtain an input impedance which is variable with the frequency if this yis desirable, by way of example, when the network is connected to a line, of which the characteristic varies in a certain manner with the frequency.

Between the different terminal couples of the network different ilter Ieffects maybe obtained.- Between the input and loutput sides of the network, i. e. between the terminal couples l, 2 and 3, 4 all the oscillations within the range of frequencies of the network are suppressed. rEhe network operates thus between said terminal couples as a band suppressing liter. Between one of said terminal couples, by way of example l, 2, lnfl one ofthe external terminal couples 5, 5 or 7, 8 respectively of the network the ordinary Yband tilter efiect is obtained and betweenV the two external terminal couples 5, 6 and 6, 8 of the two filter chains all freq-rcncics are suppressed. Y

The embodiment according to Figure el is equivalentwith that shown in Figure 1 and is differentiated from the latter only therein that the two throughgoing lines a, 7) of the network are mutuallyequal, as the filter chain is substituted by two filter chains D, E which each are connected into one of thetwo lines a, Each one of the t vo filter chains D, E is in Vsimilarity with the filter chain B in Figure l composed of two equal series impedancesl 13, 14 and 15, 16 respectively and abridgerimpedance 19 and 2O respectively... The external terminal couples of the filter chains D, E correspond-- ing-to the terminals 5, 6 in Figure 1, are designated 5, 6 and 9, 10 respectively. .The network C comprisesri'n this case, besides the shunt Aimpedance 21, the two parallel connected 'series impedances 13, 1li and 15, 16. Y Y

Figure 5 shows an embodiment of the filter chains of the network. The filter chain B is provided on its output side with a terminal impedance R2 vand includes a series impedance y1 connected thereto whereupon, counted in the direction towards the input side, shunt impedances y2, y., alternate with series impedances g/3 rlie input terminals of the filter chain B are designated e, f. The lilterchain A is terminated in similar manner with an impedance B1 and comprises, counted in the direction towards thek terminals c, d, Vshunt impedances mi, m3 alternating with series impedances 031 a,

rlh'e terminal impedances R1, R2 are so dimensioned that 'VRVR2ZC n where 7c designates a constant. The impedances acl, x2 and y1, y2 respectively included in the twofilter chains are Y so selected that the geometrical mean value If one imagines the building upof the two networks by gradually adding the different impedances a?, y to the terminal impedances R1, R2, the mutually corresponding impedances being then each time added to both lilter chains, we rind that the geometrical mean value of the input impedances in the two gradually growing filter chains will all the time maintain the value la. If one thus first adds the series impedance :r1 to Rl and the shunt impedance to y1 to R2 the geometrical'mean Value of the two impedances thus formed isequal to comply with the abovementioned condition.

A similar reasoning may be used concernnur the composition of each of the impedanccs ml, :02 etc, and y1, etc,jrespectively.

Fieure G shows diafrrarnmaticall how the impedances m and g/ may be composed -in` order to comply dition,` Each shunt connectien of two impedances in vway of example@l and a2, corresponds to a series connection of two Correspendinginipedances 1 and b2 in g/ and vice versa. lf now the part impedances @il a2, a3, etc. and 1, b2, etc., respectively in the two impedances as, QJ' now are selected in such a manner that i/all 1,/@252 ,/agbg :le one finds, by exactly the same reasoning as above-l'liat `the geometrical mean value of impedances if, composed in this manner is equal. to le. `The simplest manner to com:

ply with said condition vfor the composition of w and y is to arrange the part impedances l) in Vsuch a manner that in' each couple of part impedances al, 1 etc. the one part iinl pedali-ce` consists of capacity C and-the other part impedance of an inductance L in which case one selects =C lJywU? l C or else may the two part impedances in eaclrinipedance couple a., consists of ohmic resistances r1 and rg which have to be selected in such ainanner that '\/7'1 "2 lf all the part inipedances a, Z) are formed with the corresponding con-V by capacities and. inductances they must have the smallest possible losses because otherwise the condition of the dimensioning cannot be exactly complied with. The error caused by the loss resistance may, however,

be reduced to a very low value if the geo- Va resistance rx and /ry respectively. Provided the loss resistance is disregarded, the capacities and inductances areas mentioned so selected that l 'l l z ,C Oy Ox In resonance y To make the geometrical mean value of .r and y equal to c also atV resonance one must i In order to make the influence of the loss resistances upon the conditions for the dimensioning so small as possible also the loss angles of the inductances Lx, Ly must thusvbe equal which may be obtained, by way of example, .by providing the inductances with equal iron cores and equally large winding spaces.`

` In the deduction of the formula (7) tie assumption is made that theinput impedances X2 between the terminals c, Z and e, ,t respectively in the filter chains in Figure 5 coincide with the characteristics Z1, Z2 between the same terminals, i.e. that the filter fchains terminate relectionless in terminal impedances dimensioned inV corresponding manner.

lnpractice `it is of course difficult to design suitable terminal impedances which at all frequencies terminate the filter chains re flectionless. `A condition for this is that the terminal impedances for all frequencies are equal to the output characteristics of the filter chains.` Thedesired result that the input impedance of the network should be independent of the frequency may then, however les lil

as explained below, alsobe obtainedv without terminating the filter chains inf-this mannerrefiectionless. Y

The input characteristic of the two filter chains A, B in Figure 5 may', accordingto the Equation 3', A', be expressed in the following manner:

As before'is asumed that I 1=p2=-p u In the same mannerk one Vobtains .for the output characteristicof the two filter chains at the terminals 5, 6 and 7, 8 thevalues y p1 an Rd2-p a2=the line angle Afor each filter. section in the filter chain B.-A n Y p1=the reflectionattenuationconstant of the filter chain A. Y i p2=the refiection attenuationconstant ofthe y filter cha-in B. Y g1=the refiection line angle of 'the Y filter chain A.

, g2=the reflection lineiangle kofthe lter chain B. Y itl-fthe number of filter sections of the filter chain A.

1i2=the number of filter sections of the filter l chain B.

The absolute values of the input imped-I ances of the two filter chains A, B at the terminals c, l and c, 7 respectively will be (compare Elektrische Nachrichtentechnik' volume 5, Number 5, 1928,v Ueber das Nebensprechen und andere damit zusammenhngende Erscheinungen, Laurent) cosh2 (mz +212) i,- cosZ fazn'z g2) The phase angles of the impedances are (IDX: @Zi arctg sinh 2 17111 +271) sinh 2 (am +132) If one now makes ,31.7L1: ,82mg and alf/L1:

'Y where n is an even or an oddnumber.

is readllyunderstood from the above menagit, by way of eXample, by making thel filter chains withthe same propagation con# 'Y stant for each filter section and the sam'e number of filter sections, whereby tioned article in Elektrische l\Ta'Cl1richtung` technik we furtherhave Thus is e2 pl+yq1= Anzge and i e291 2202 ezjgi: ezjgz This means that.l

If said values inthe above expressions are inserted for the absolute valuev of the and, upon the insertion in the expression for the phase angle of the impedances,

` vIf the geometrical mean X1-X2 is calculated from the vFormula v(2) the absolute value of the input impedances y w/ (R1) (R2) (8) For the phase angles @Zof the input impedancesione obtains, if @Rp @R2 and FD,

are the phase angles of the quantitiesY 1,v R2 and-.p1 i

The quantity Z acts thus, as in the previous Case, as an ohmic resistance. The re- -sult involves that the refiectionswhich are representedby p1, and gl, g2 compensate eachother 1n the geometrical mean..

provided thefilter chains are terminated by R1, R2. i l i Figur-e 8 shows an embodiment of a network vwhich includes a differential transformer and is arranged .in symmetrically `bridged l 'connection. The one H ofthe series connected, the two coil couples -be.`

. ing each'included in one of the two lines the primary coils L1 to L.l and the secondary c, b of the network. The shunt impedance 17 is connected between the middle points of thetwo coilcouples.4 On account of the tight magnetic coupling in the transformer said transformer introduces no self induction and n0 iron losses but only as small Vdirect current resistance in the filter chains. `The filter chain I comprises both Winding L5 in the differential transformer and also the `bridge impedance f8 connected to the lterminals of the secondary windings. The filter chain I is connected over the differential transformer in the same manner to the two lines a, of the network whereby the symmetry of the connection is obtained. Said networkmay be advantageouslyv used in two-way amplifiers or the like, a line or a line section being connected tov the fter minals 4 and a nco'rrespending line bal ance to the terminals l, 2. To the external terminal couples 5,. 6 and 7, 8 of the two filter chains I, H may, if desired, 'onesende ing circuit and one receiving circuit, or the amplifier circuits each corresponding-to yone talkingdirection of a repeater, be connected.

Figure, 9-shows diagrammatically an embodiment of a two way amplifier according to the invention. To the terminal couples g, 77 and i," the lines or line sections may l be connected. The correspondingline .bal-;

ances are designated N1, N2.

Two'. amplifiersVnVQ each T1 andJTL and over filter chains K1', K1, The filter chains K1, K2 form together with the differential transformer T1 a network accord ing to the invention and the filter 4chains K1,'K 'form together with thedifferential transformer T2 another similar network..

As seen from the figure the filter chains K1, I Y i n c i n c K2 on the:. sides facing the `differential transformer T1, have" T-characteristic and vr-characteristic respectively and, on the opposit'ev sides. `also 'VT-,characteristic and 1r-` for one talking direction` yare connected over dnferential.transformers characteristic respectively. The two filter .chains on the opposite'side of the amplifier' vare arranged in similar manner. In this Vdisposition the twofilter chains have thus in c each ofthe networks by way of example 1 K1. and K2 mutually different characteristics on both sides. The two filter chains have also the samenumber of half filter se"- tions which number may be even as well as odd. c

Figure l() shows a practical embodiment for the applicationof the invention in a twoeway amplifier. Inthe figure only such parts are shown which are necessary for the understanding of the circuit arrangement. rlhe'arrangement comprises two amplifier valves V1, V2, one for each talking direction. .The talking directions are indicated by arrows. The anode side of the valve V1 and the grid side of the valve V2 are connected over corresponding filter chains to the differential transformer T. rlhe filter chain connected to the valve V1 comprises, besides Vthe differential transformer, on the one .hand a coil L.. connected in series with the secondary winding of the differential transformer and, on the other, a condenser Ca bridging the primary winding of the transformer. In the filter chain connected to the amplifier valve V2 there are, besides the `differentialtransformer commen to both filter chains, included a coil vLg 'connected to the. middle point of the primary winding and a condenser Gg connected in series thereto... If the differential transformer, as assumed, has a very tight coupling between 1 two-way amplifieris connected.V To the opposite terminals ofthe network a correspondingline' balance N'is connected. Between the valve V2 and theappertaining filter chainan input transformer T.- having a comparatively high primary impedance is connected into circuit. The 'oscillations incoming from theline over the terminals g, 7L are supplied to the 'input transformer Ti over the corresponding "filter chain 4and a poteI-rtiometerlD connected to the output terminals of the filter chain. As seen from the figure the filter chain lyingbetween the line and the anode side of the valve Vli'has, on the side facing the terminal couple g, le., a 7r-characteristic whereas the other filter chain on the side facing saidV terminal couple has a T-characteristic- As an example'of the practical application of an arrangement'according to the invention the dimensioning of the above described 'amplifier accordingto Figure lO is given.

iov

case evidently a parallel to the terminal im-i pedance R1 whereas the potentiometer resistance Bp corresponds to the terminal impedance R2 in Figure 5, providing the pri. .mary winding of the input transformer Ti has a high impedance. For the series and shunt impedances of the filter chains in the arrangement in ,Figure l0 the following equations are valid.

Si :jOJLl l 41 S2 :jbJLg From this follows The condition (6) mayl in this case be expressed as follows The impedance of the line balance N must f obtain the following value in order to suit the line, of which the characteristic is related to Ra, Rp as indicated in Equation (8) The three first conditions may immediately he complied with. The fourth condition may immediately be complied with for free overhead lines and weekly loaded cable lines and may in other cases be met by a suitable line extension. Y

' Figure l1 shows an embodiment of .the network according to Figure l. rlhe filter chain B includes, counted from the enter? nal terminals 5, 6, a series capacity composed of two series connected capacities CB1 the secondary windingv LB of a transier T, of which the primary winding Lm ded into two equalparts forms the common part of both filter chains, and finally a capacity'sliunted to the primary winding ylim and consisting ,of two series connected condensers- (lf2. The filter cha-in A includes, counted from the output terminals 7, 8, a shunt condenser `UA1 a transformer TA and a condenser CA2 connected in series with the primary winding of the transformer, and finally the two winding halves of the primary winding Lm of the transformer T in parallel connection. As may be seen from the figure the parallel connection of capacity and inductance in the one network corresponds to a series connection of inductance and capacity in the other network. To obtain the best possible energy utilization the network is so dimensioned that the impuef dance ofthe network at each one of the terminal couples l, 2 and 8, el is equal to lo, between tlie external terminals 5, 6 of the lter chain B equal to 27;, and between the external terminals 7, 8 of the filter chain A equal c to rlhe inipedances of the apparatus connectedoto the terminals 5, 6 and 7, S mustV also be equalto 21a andlC respectively. The

oscillation energy, having frequencies within the range of frequencies-of the filter chains and introducedat the input terminals l, 2 of the network, distributes itself according 'to lc the terminal iinpedances 2k 5 respectivel, 2 is V, the voltage between the terminals 5, 6 will be equal to V and between the terminals 7 8 equal to Strictly speaking this 110 is, however, correct only for the middle frequency of thefrequency range and at ratios of l l of the two transformers TA, T.

ln the embodiment. according to Figure 1l is it generally possible to utilize only the energy received at the external terminals 5, 6 and 7, 8 of one of the filter chains A or B, i. e. only one lialf of the supplied energy. A complete utilization of the energy supplied may, on the other hand, be obtained in the embodiment according to Figure l2 which is differentiated from the connection in Figure 11 in that the output sides of the two filter chains A, B are parallel connected. Said parallel connection is rendered possible without loss of energy by that the ratios of the two transformers are so selected that the voltages on the output sideof the transformers are mutually equal. rlhe ratio of the ifo transformer TA, counted from Vthe output terininals,will be, by way of example,selected half as high as the ratio in the transformer All It must, Vof course, be observed thatthe connectingtogether must be made so that the two Voltageshave the saine phase. In the connection shown in Figure 12 `of the terminals 5, 6 and 6, 8- it is assumed that the .primary and secondary windings of the 'Mansformers are wound in the same direcw voltage for each transformer," i. e. the volt? ages at the terminals 5, 6 and 7, Swill beV tions. Y p

lf the ratio LA ofthe transformer TA is equal to 1:2 and the ratio [i of the transformerT is made equal to 1: 1 the output equal tothe supplied voltage` V between the terminals 1, 2. The network impedance at the parallel connected terminal couples is Figure 13 shows asimilar arrangementfor utilizing the entire energy supplied to the ldifferentiated,from that in Figure 12 `sub stantially therein that the output sides of the two filter chains A, B in this case are series connected. One may, by way of eX- as follows. A

Aizi

, F211 Y. The impedance of the-network between the terminals 5, 6 is in this case The impedance-,lc between the input terininals l, 2 of the vnetwork according to Figures 12, 13 is constant at all frequencies as in a network, by way of example according 'j to F igure 11, in which there is no joining of the external terminals ofV the twoV filter sliifted the conditions are reversed, i. e. the impedance between thel terminals 3,741` will be constant at all frequencies whereas the impedance beweeii the terminals 1, 2 will be constant only at the frequencies outside the range of .frequencies of the filter chains.

In certain cases, by way of example in cascade coupling of several networks, it` of great importance that the impedance both on the input side and on the output side re- ?.l of the net I will `be Zero.

input terminals k1, 2 of the network and is ample,select the ratio of the transformersnections between the terminal couples are f mains constant. ln the arrancement according,` to Figure 14E this is attained by con-4 Ain the composed network are all dimensioned for the same range of frequencies. lf the oscillation energy is supplied to the input terminals '1,2 of the network l, it will be transferred under equal distribution to the two terminal couples 5, G and 7, 8 to the other filter chain whereas, on the other hand, the voltage between the output terminals 3, The windingr directions in the transformers TA and T are assumed to be so selected that the oscillations incoming,` to the filter chain Il from two sides and having mutually equal energ (ompensate the mutual effects in relation to the input terminals 1, 2 of the network ll whereby the voltage between the latter will be Zero whereas the oscillation amplitudes areadded as regards the output terminals 3', 4C', of the filter chain H. As the oscillations from the one network to the other is transferred completely symmetrical as regards the input terminals 1, 2 and the output terminals `3, 4lof the network l, the impedance between Vthe terminals of said two terminal couples will be constant at all frequencies. To render Vpossible a connecting` together of the different filter chains without energy losses tlieratio of the transformer TA, .l, TA, T, counted in the direction towards the external terminals of the filter chains, must be so selected that eigen #A MB where MA, ,aA and im, an designate the ratios of the filter chains A, A', B, B respectively, To make the impedance Vbetween the terminals 1, 2 and 3, 4 equal to iti and the iinpedance between the terminals 3, l equal to and 7e, k constant at all frequencies, it is required r that where ZA, A ZB, ZB', denote the impedances at the internal terminals of the filter chaii'is A, A', B, B at the middle frequency of the frequency range.V A similar `network cogmposition acts thus between its terminals 1, 2 and 3,', el and between the terminals 1, 2

and 3,"4 or vice versa as an ordinary band filter, Between 'the terminals 1 2 and 3 4, 1 2 and 1' 2',`3 4 and 3' 4' kthe network acts 'as a `band suppression filter' forsaid range of frequenciesof the 'lter chains. Thereby that the' impedance both between the terminals 1, 2 and between the terminals 3, 4 is independent of the frequencies, several similar network'compositions may be seriesl connected without having any mutual disturbing influence. Y

In Figure 15 there is'shown' another em-` bodiment and combination offt-he arrangements described with reference to Figures 12 and 14. The two filter chains A and B are substantially built in a mannersimilar to that Vdescribed in conjunction with ythe above networks. By ytaking certain measures it is attained with only one'network is required to attain the sameresult as in the arrangements according to Figure 14. The network consists of two filter chains A, B dimensioned yfor the same range of frequencies, each having a ratio of transformation aA, aB, counted towards the external terminals, ,as being then equal `to 4M and the impedance between the internal ter-y minals of the filter chain A being and the impedance of the filterchain B being ZB=2Z0 where denotes theimpedance between the terminals 1,2, and v3, 4 at the mean frequency. of the frequency range. The secondary` winding of the transformer T1 is divided. into equal parts and the middle point a 'is connectedto the terminals 6 of the ,filter chainy BjfSaid compensating arrangement may also be. obtained by that the condenser C5 is divided intotwo equal series connected condensers the middlel point a being branched off' betweeny 'the two condensers. Besides theterminals 1,2 and 3, 4 the network is further provided with two terminal couples 1', 2'and 3", 4', of which 1' is connected to the terminals 7, 2' and 4 to the terminal 5, and 3' .tothe lterminal 8. d If and the volt-age between'the terminals 3', 4"`

frequencies.

lines at theterminals 5,76' band Vfilter operay tion is Vobtained between 1, 2 and 1", 2', and 3,4 and 3', 4', and band suppression operation between 1 2 4', 1-' 2"`and 3'-4', and 1' 2' and 3 4. If the network, as` in the preceding eX- ainple, is so dimensioned thatthe impedance between Ithe input and output terminals 1, 2 and 3, 4 is equal to la the impedance between the terminals 1', 2' and 3', 4' will be vequal to A2M According tothe invention is is constant at all frequencies.

f In `Figure 16 an example is shown how the network, described in connection with Figure `15, is arranged `when connecting vsender and receiver for high frequency telephony to an ordinary,l telephone line. The arrangement is composedy of five seriesor cascade connected networks I, II, IILIV and V. `The network composition iis, on

the one side, between the terminals 3v, 4V

connected to a: commonlineLjand on the other side terminated by aterminal imped-V ance 7a. As the impedance between the terminals 3V," 4v is constant at all frequencies the line L may obtain a reflectionless termination at'allfrequencies. Each Vone of the dierent networks I to V is made according lto-Figure 15 and the series connection of thev network 'may take place without energy losses or refiections because the impedance between the input and output terminals 'of each network is constantr at all To the 1H 2H' etc. impedanceslRl, Ru are` connected. To the terminals 31', 41' of the network I a lowfrequeney line LF is 'connected@V 'l The terminals 3H",s4i1v", andw', 41V' 'of the networksvII' and'IV are each connected to a sender SH and Swrespectively for high frequent signals and the terminals 3m', 4m' and 3V', 4v' of the networks III and V are' each connected to one receiver MmL and y Mv for'high frequencysignals. If the different networks areVv dimensioned each forv l over the same vline L without disturbing withfonly a negligible attenuation through the;V network V, IV, III, II are rec'eivedjby the network I, from the'terminals y 31', '4f' ofA which they are forwarded to the line High frequent signals vwithin drf- Y ferent frequencyqranges are lreceived by the Y networks V, IIIVthe Signals designatedkfol the, lat'ter ,networkA passing throughV and IV with only a negligible attenuation and vwithout disturbing thereceiver Mv; Signals from `the line LFto thenetwork I are so directed thereby that they pass only to the right Vthrough the remaining networks II,

III, IV and V to the line L and not to the .left to thewterminal impedance In the` same manner high frequency signals are sent from SH' and Sw. A signal sent vby way of example from Supasses through the filter chains of the networkII over its terminals 3H, 4HHthroughIII, IV and V to the line L. The directional action in comunetion with the filter action of the filter chains bring about that no energy passes through` a the network Ito the left.

In loading a line itis, asknown, desirable to attain a lso high loading as possible kto reducek thereby the attenuation as far as passible.` As, however, the limiting.fren` i'. quency of: the line decreases according Vasv the loading is increased andbecause thereby the rising or falling part of the characteris-- ticcurve more andL more vis displaced down-` Y wards towards the speech frequency" range.

Thenfange for constant- .characteristic uponf an increase of `Ythe loading, reduced, whereby the speech transmission gets bad. Thedegree of loading is thus rather limited.

' By` the embodiment of the inventiongas j ered` possible independently of said ,diseV shown iii-*Figures 17 andrlS a considerable increase of the loading is, however, rendplacement of the characteristic curve. This is obtained by making `the loaded line to 4forni for to, be includedy as a part in theone filter in the impedance network whereas the li ne or apparatus having constant characteristie is connected to the` input terminals of l theV impedaneenetwork. The latter line or nal 4couples form the input `terminals of the apparatus may thus be ,connected reflection- U less tothe loaded line.V g 4According totheinvention the impedance network is preferably formed ,inv conjunc- `tion with av differential transformer, fof

-which the two mutually symmetrical terminetwork or the terminals of a .line vbalance whereas the vone ofthe two other terminal couplesof the kdifferential transformer, by

way lof "eizamplefthe terminals ofl theun-V di'yided' transformer winding, are connectedV to the pupinized line and the .othenb'y way '.ofneXample the-,middle nitiappings, are connected tola filter, the characteristic of whichA varies `with the frequencyin 'a'manner opvsection of lengthf menos;

possible the reiectionless connection of a 4quad connection consisting of two loaded lines to a ltwofwire connection having a constant characteristic. l v

One embodiment of such a connection is shown in Figure 17,'the two talking paths in the quad wire connection being used for mutually opposite talking directions, whereas in the connection shown in Figure 1S the two lines in the two-wire connection are parallel connected` and vform together a single talking path.

.1 The differential transformer connecting element between the lines is connected by Aits mutually symmetrical terminal couples l, 2 and 8, 4f respectively'on the one side to the free overhead line .L and on theother side, to la line balancefB having thev same impedance as the overhead line L. To the middle tapping of the differential transformer the one loaded line L1 is connected whereas theother'loaded line L2 is connected to the undivided winding lof the differential transformer. YThe one loaded line Ll is, ladjacent to the differential transformer, terminated by an undivided line section,'i.` e. a line portionhaving a length .equal to'an entire coil distance s, and a load coil `p connected thereto, the inductance of which is half as jhigh as the inductance of the `load coils P out on the line. line represents thus a T-filter i. e. a iilter having a falling characteristic. `V The other loaded line L2 is adjacent to the differential transformer` terminated by aY half loaded wir@ and represents a i-ltei, i. e. a filter having rising characteristics. Ifthe two lines other- 1 wiseA are similar and loaded with equal load coilsfP and geometrical means oftheir characteristics, counted from the differential transformer, will be constant. Said geometi'ical means should, according to the invention, be or, by suitably disposed line eXtensions, he made equal to the impedance of the line balanceI The, input characteristic of the f network consisting of the differential 'I serving as Said loaded i' transformer together with the loaded line L1 and L2V between the terminals l, 2 is under i said condition constant and equal to the characteristic of the line balance.

' The two loaded lilies are assumed to torni, `in the shown embodiment, each one talking 1169. former T and provided with va corresponding 'path in the Vquad wire connection and inline section s and a thereto `connectedload.

coil P having half the normal inductance whereas the line L2 is terminated by a half line section In the `connection shown in Figure 17V the load coils on the Vone line in the quad wire connection are displaced half a section distance in relation to the coils in the other line which involves certain practical inconveniences and results in increased costs of erec tion. Said inconvenience may, however, be eliminated without difliculty by providing the one` of the twopupinized lines adjacent tothe differential transformer with a line extension representing a corresponding diS- placement of the two lines in relation to each other. An embodiment of this kind is shown in Figure 18 where the load coil P of the twoY loaded lines are disposed opposite each other. The line `L2 is connected to the differential transformer T in the samemanueras in Fig ure 17, i. e. it is terminated adjacent 'to the differential transformer by ahalf line section The v'line L1 is also terminatediwith half a line section which, however, is provided with a line extension" F. Said line extension consists of a shunt condenser C', connected into circuit next to the line and havinga capacity corresponding to the line capacity of half a line section, and a series inductance 2J the size of which is equal to half .the inductance of the load coils P on the line. i If `desired, the line extension may also enclose series resistances R, corresponding together to half the ohmic resistance pro line'section. Bvtheaddition of the line extension 'F the line L1 functions, counted form the differential transformer, inexactly the same manner as ythecorresponding line in Figure 1.7, i. e. asa .T-filter.

The quad wire connection is by itsop-vl posite 4end connected in similar lmanner. to-

another overhead line L or anl apparatus having vconstant characL former' T of the same kind as the .transconnection of T as the line L2 at T is termi nated byk a line extension F and connected:

teristic lwhich con-*jv nection is vmediated by a, differentialt ansto the 'Iniddletapping' Iof the differential transformer whereas. the lline L1 instead is connected without line extension to the undividedl .Winding of the differential V`transformer. The elements C', 27', and R of the line extension F are thesame as the corresponding elements in F. Both lines proper terminate by a. half section length In Figure 18 the two lines L1, L2 are .evidently entirelyvequivalent and may form in cominon a single talking path consisting of the two lines in parallel connection. In spite of the factl that four lines are used for the l transmission of speech current in only 'one naryfdouble line is,l a-sknown, s R GZ ,ff-mt T Where R is the ohmic resistance perV kilometer, Z the line characteristic, and G the leakage per kilometer. Y

Theslsecond term `on the right hand side in the `formula may be neglected because G is very small, only about 106, and the term in question may, evenfin the worst case,` Y

represent at most about three percentr of the total attenuation per kilometer. From the above formula we make the conclusion that the quantity R may be doubled without increasing the attenuation ,8, provided Z is simultaneously doubled. Thel cross talk in lcables'is,as known, substantially'a function of the voltage which in turn is l/:ZI where I is the amperage. As in this case the current in each line is reduced to one half, one `may thus make the characteristic Z twice as highas normally without altering the'voltage V and each line L1`,.L may thus be loaded to a characteristic twice as high as that of an ordinary line without, however, increasing the cross talk. If one thus doubles R by reducing the area of eachr coil without inconvenience maybe YmadeV with a smaller iron core and a thinner wire. Such a quad wire line does notv take up a considerably larger space in a cable than a by a quad'wire twisted in .this manner in` a cable fw'illnot be considerably larger than the space'taken up by twowires 'which are twisted according to the method of Dieselhorst and Martin. l r

A line made according to VFigure 18 is .particularly suitable to beused in long distance telephonyV or for the transmission'of music. f f 'T lVeclaini:- a l 1. An electrical network comprising yin combination afilter B having itsterminals Y of the one side connected withfone= input l Vseries impedance of a second filter including. said `artificialline7 the meansquares of' the` terminal and. one*,outputlterininal of the network and including an impedance l1, 12 shunted between said terminals, aquadripole 17 having one of the terminals on the one-sidel connected to a middle-tapping on said impedance and the-other terminal of combination a filter including an impedance shunted between its terminals on one side, said impedance being provided with a middle tapping' and forming auseries impedanceY ofthe ,network, an artificial line connected between the symmetry points of,.:the Atwo branches of the network, said impedance of the said filter, forming two y branches of a Y characteristics ofy said two filters on the sides at which they lare associated with one another being independent `of the' frequency. A 3. An electrical network comprising vin combination an-iinpedance having a middle tapping andforming a; series impedance of the network, a first artificial line connected with one pair ofv terminals tothe4 ends of said impedance, a-sec'ond artificialfline connected with one terinfinalto the iiiiddle tapping of'said impedance and with theother terminalV of the saineside to one input ter-f minal and one output terminal of the network, saidlimpedance forming together with thefirst artificial line a first` filter while the l two halves of said impedance-form paralistic and `T-characteristic respectively, on,

'quency A c Y s Y f An 'electrical network comprisingin` combination'a differential transformer con@ rlel branches'of" a series impedanceof a second filter including the secondartificialline,

said filters accordingly havingv Tr-characten the sides atwhich they are associated with one another, the mean squares of said chai-1 acteristics being independent oftheV `frenected betweenone input terminal and one output terminal of the network, airst filter connected to the one side of said differential transformer, a second filter connected with one terminal to the middle point of the transformer and with the other-"terminal of l tl'i'esame side to one input terminal and one output terminal of the network, the mean square values of the characteristics of said filters on the sides associated together being substantially independent of thefrequency. c,

5. An electrical network as claimed in claim 1, characterized in that the lters associatedtherein are so dimensioned that/their characteristics at the ends at whlich they are 2 spectively at the middle,` frequency within the frequency range of thel filters, whereby the impedance between the input terminals and between the output terminals of the network will ybe equal to lc, said quantity being aconstant.

associated with one another are and 27a re- Y V6. An electrical network as claimed in f claim l,\characterized in that the; complex propagation constants of the filters associated therein have the saine value at all frequencies. i Y l `7. An electrical network as claimed in claim 1, characterized in that the filters are provided. with end impedances which are constant orV substantially constant and so selected thatv the reflections at said impedances substantially compensate each other. 8. An electrical network as claimed in claim l, characterized in that the end impedances of the filters are so chosen a-s to establish substantially reflectionless connections at the end terminals of the filters.

" 9. An electrical network as claimed in claim 1, characterized in that the geometrical means of the characteristics of the two filters at the `ends at which they are asso# ciated is. substantiallyequal to the impedances connected to the input and output terminals of the network.

l0. An electrical network n asl claimed in claim 1,characterized in that a transmission nected to the network on the other side, send# ing and receiving apparatuses being connected tothefree ends ofthe two filters.

11.An electrical networkcomprising in combination a filter having its terminals of the onefside connected Awith one input terminaland one output terminal ofthe network and including an impedance shunted between said terminals, a quadripole having oneof the terminals on the one side connectedvto a middle tapping on said impedance and the othei` terminal of the saine side halves of thesaid impedance forming two parallel branches of a series impedance of line is connected to the network on the one vside and a corresponding line balance is conconnected withone inputterminal and one `output terminal Y ofthe network,;the two Y lle a second filter including the said quadripole, the mean squares of the characteristics of lsaid two filters on the sides at which they are associated with one another being independent of the frequency, and transformers being included in the lters, said transformers having their ratio of transformation so chosen as to transmit an incoming` oscillation with equal voltages to the end impedances of the filters. c p

12. An arrangement as claimed in claim 11, characterized in that the ratio of ytransformation in the filter commencing with a shunt impedance is one half of the ratio of transformation in the other filter.

13. An arran ement as claimed in claim 11, characterize in that the two lilters are joined in series connection at their free ends.

14. An arrangement as claimed in claim 11, characterized in that the two filters areI joined in parallel connection at their free ends.

15. A circuit arrangement composed of two networks, as claimed in claim 11, said networks being connected in such a manner that the external terminals of mutually corresponding ilter chains are connected to each other.

16. An electrical network as claimed in claim 11, characterized in that the lter having T-characteristic includes a dierential device the middle point of which is connected to the one end terminal of theother filter, and that by the connection between the lters there are formed two terminal couples and from each one of the end terminals of the filter first mentioned and the free end terminal included in common in the two terminal couples in the other lter.

17. An electrical network as claimed in claim 1, characterized in that the two filters associated therein are composed of equal numbers of impedances corresponding to each other two and two in such a manner that the mean square of the two impedance values of each pair is equal for all pairs of the impedances.

18. An electrical network as claimed in claim l, characterized in that the two ilters associated therein are composed of equal numbers of impedances, each shunt impedance in the one filter corresponding to a series impedance in the other lter in such a manner that the mean square of two corresponding impedances is equal for all pairs of corresponding impedances.

19. A circuit arrangement composed of a number of cascade coupled networks according to claim 1, said networks being dimensioned for different frequency ranges.

20. A circuit arrangement composed of a number of cascade coupled networks according to claim 1, said networks being connected at one end to a transmission line and at the other end to a corresponding line balance, and sending and receiving apparatuses being connected to the two filters associated in each of the networks.

21. An electrical network comprising in combination a filter having its terminals of the one side Connected with one input terminal and one output terminal of the network, a quadripole having one of the terminals on the one side connected to a symmetry point of said ilter and the other terminal of the same side connected with one input terminal and one output terminal of the network, the mean square of the impedance between said terminals of the filter on the one hand and on the other hand the impedance between said terminals in parallel connection and the opposite terminal of the quadripole on the side associated with the filter is independent of the frequency.

22. An electrical network as claimed in claim 1, characterized in that the two lters associated therein are composed of equal numbers of impedances, each shunt impedance in the one ilter corresponding to a series impedance in the other filter, and that the mutually corresponding impedances are built up each of an equal number of part impedances in such a manner that the product of each part impedance of the one filter and the corresponding part impedance of the other filter is substantially constant at all frequencies.

23. An electrical network as claimed in claim 1, characterized in that the two filters associates therein are composed of equal numbers of impedances, each shunt impedance in the one filter corresponding to a series impedance in the other filter, and that induction coils included in the corresponding impedances are dimensioned for the same loss angle.

MAURITZ VOS. TORBEN LAURENT. 

